servers:
  server1: &s1
    - ADDR=172.16.0.1
  server2: &s2
    - ADDR 172.16.0.2

ping: &ping
  - ping $ADDR

windows:
  - s1:
      - <<: [ *s1 ]
      - <<: [ *ping ]
  - s2:
      - <<: [ *s2 ]
      - <<: [ *ping ]